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[Marks DTM Calib]

Lol............the phrase 'blind Alley' springs to mind!

Right error code 15:

15 - Coolant Temperature Voltage High

Now....this could well explain some of your symptoms.

If the ECU is not able to determine the coolant temp correctly then it might not run on the cold start cycle which will make it like trying to start a carb car without a choke!

Similarly, when hot it might be runing to rich!

As always, number one rule..........fix the obvious first before divng down blind holes!

Ow ye, your bound to get decreasing revs if you pinch the pipe to the idle valve....as you will be limiting the idle air!

Might be worth considering cleaning the idle valve whilst you are at it.

And yes, the coolant temp sensor is at the back of the V!  

[Abiton]

Not sure about the V6 version, but the ICV on mine is a solenoid with PWM'ed (12V?) drive, I'm pretty sure.  

You could do with Tech2 looking at your CTS output to see if it's discrepant with the real temperature of the coolant.  Check the wiring to it for breaks/shorts if you can.  One side is grounded t'other side goes to an ECU pin.

[daveball]

Thanks for all replies.  I'm still confused and nothing is clear cut. The error 15  I presume is intermittent as the engine management light goes on and off i.e. don't believe error 15 is constant. When I get excess revs management light is off so I assume the temperature sensor is working correctly at that time. I have the suspicion that the temperature problem is an intermittent connection, it only happens after the car has been driven some distance and I recently stripped down the inlet manifolds to sort out a water leak. I noiced the connector to the temp sensor was loose and corroded due to the leak and cleaned and tightened the clip but I wasn't totally happy with it. It might be the error 15 problem, ocassionally going open circuit at the connector. Anyway as stated when the excess revs occur the engine management light is off. The car has been running for several days with the occasional error 15 but No excess revs.  I'm not totally sure but doesn't this mean that the excess revs are not caused by the temperature sensor problem.
I know with cars that nothing is ever certain but this seems logical.  

If the ICV is driven by a 12 volts PWM signal does anyone know the characteristics , i.e. frequency and Mark/space that would be expected around tickover at 500 RPM say. If I know this I can look at the signal and decide if the ICV is at fault or something else. I don't feel the the two faults are closely related and I would like to have some idea whats happening round the ICV before I immobilise the engine by stripping the inlet down to get at the temp sensor. I do know I have to do it sometime.

A final question, when do the stored error codes get cleared, or do they need to be cleared by some external means.


Dave

[Abiton]

Dave, w.r.t. the code 15, I think you might be looking at it sort of backwards...

When the EML is lit, the ECU will plug in some default value for the coolant temperature, ignoring the out-of-range reading. Car will probably run OKish.

When the dodgy contact (if it is that) is giving a reading just within the expected range, the EML will be off, but the temperature the ECU is working to may be far from reality.  (Much colder?)

With the ICV, if you've got any sort of PWM signal at the connector I'd say the electrical side of things is OK.  It's the air passages inside the valve part clogging with crud that usually causes the probs with these things IME.

No idea on the characteristics of the PWM, but it'll be in some sort of closed-loop thing with ECU looking at revs vs open/closedness, so it'll be whatever it needs to be to achieve the nominal revs (as far as it is able to within its operating envelope).

HTH
Pete

[JamesV6CDX]

Now I've got to the stage of being able to control the revs down to stall by cutting off air to the Idle Control Valve;  doesn't this imply either the ICV or the signal controling the ICV is faulty. The crunch comes now. I am an  electronics (industrial electronics) man by trade. I can measure anything electrical and understand it, BUT! how does the ICV work, is it a purely analogue voltage drive, or is it pulsed, and what voltage waveform and level should I expect if I monitor its connections. If its an analogue valve, I should be able to apply a variable voltage to it and see if it opens and closes, if I knew the voltage range required. I could experiment but I don't want to "$%$^"  it completely if its ok.

The last question is does the error code 15 have anything to do with the fault or is this totally a seperate issue???

Dave

If 15 is coolant sensor I would think seperate issue. CTS will just put it on a default map, not cause it to run that rough.

I still think it's an air intake issue - ultimately, if the unmetered air wasn't getting in, it wouldn't logically be able to rev that quick with the throttle closed, if it wasn't getting the air from somewhere.

Have you had any work done recently on the air inlet?

Try pulling the ICV connector when it's idling, see what happens then.

Never seen it before on a V6, but I guess the valve could be mechanically stuck open?  :-/

[daveball]

I think you have hit the nail on the head. If the idle process is a closed loop and the only thing that is faulty is the coolant temperature reading wether it be wrong within allowed limits, open or short circuit, then the ECU should adjust the ICV to give a sensible level of RPM i.e. 500- 1000 RPM. It gives 2000 -2500 on my fault which makes an automatic car a bit dangerous. At 2000 + there' enough power to make the car very difficult to stop. I can't believe the control system would allow this if it were still in control even with a faulty sensor, unless it were the crank sensor. In my case this is not so or at least its not reported. So-oo I think its more than the temperature sensor at fault. I've been backing away from dismantling stuff cos at the moment the car isn't under cover. Should get the mess of a garage cleared tomorrow and will start some practical work rather than theory. I will start by checking the input to the ICV before I dive into the temp sensor problem.  

Just as an aside, the amount of hose constriction I need to apply to drop the revs to around 500 is almost totally flattening it. I can only believe this means the ICV is wide open either due to incorrect input or faulty/dirty valve.

 Life would be so much easier with all this electronics if there were good wiring diagrams showing both connections and how wires are routed . I could replace the temp sensor with a suitable resistor/semi-conductor to test correct operation and save a lot of dismantling.

Dave

[daveball]

Just seen your post james. I think you are right about excess air and it not being the fault of the temp sensor. The fact that I can control the revs down to nearly stall by squeezing the ICV input pipe surely means there is no leakage anywhere else. So it must be the ICV stuck open either cos its driven open or its dirty or faulty.

Yes I had the whole inlet system off 10 weeks ago to replace the HBV and its hoses. But I think I did a good job with new gaskets and all pipes tight, and its run for some time OK.  As I said it was then I wasn't happy about the temp sensor connection, and I will have to do something about it, but I still think its not connected to this fault.

Regard Dave

Dave

[philhoward]

Dave,

If the EML is on, and a CTS cods is stored, then i'd say its pretty sure to be the CTS - either a high resistance (bad connection) so it drifts in and out of what the ECU expects or intermittant open circuit (broken wire).
The ISCV does work via PWM (for some reason 2kHz, and changing mark/space ratio springs to mind), but guess that it would look like an Analogue value to a good old AVO 8.

If the ECU thinks its cold (the temp sensor is NTC), then it will try and raise the idle speed, hence the increased rpm.

[Marks DTM Calib]

Your over complicating things!

NUMBER ONE RULE OF DIAG - Be systematic and address the obvious faults first!

So sort the temp sensor, this will then give you a better understanding of what realy happening as the ECU light will now only come on when one of the other faults arrises.

[daveball]

Well today I got stuck in.  Checked back from ECU with ohmeter between pins 30 and 45 of ECU connector ( Haynes Manual). Gave open circuit. Great I thought error 15 cause. Dismantled plenum and inlet manifold, diconnected temp sensor( with 2 pin conn), thought just check wiring back to ECU pins 30 and 45, OK 0.4 ohms as near as my meter reads. Waggled wires and loom, still 0 ohms approx, must be duff sensor I thought. Couldn't reach pins in situ so removed sensor. Guess what! Reads about 2.9K ohms, and reduces as I warm it in my hand. This sounds OK to me. Now get reading back from ECU of 2.9K or so at pins 30 and 45 and this is solid bashing sensor and waggling  wiring. Sods Law. I'm going to put a new sensor in tomorrow when I get one, but I'm not hopeful that I'll solve the problem. There's no corrosion on the sensor pins or the connector so why was the EML intermittent.

I monitored across the ICV connector for volts and waveform, its 0v flat line with ignition turned on but engine not running. Should there be a control voltage there with engine stationary??  The ICV reads about 9.0 Ohms, is that about right?

If I solve the error 15 fault will the code be removed from the memory or does it have to be reset somehow.

Regards Dave

[JamesV6CDX]

Hi Dave,

If it's not seeing a  value from the CTS then the EML will go off....

[daveball]

Thanks for the reply James. Probably didn,t ask the question in the right way. What I want to know is if I clear the fault cause, will I still read out the error 15 when I do the paper clip test, or does the fault memory need to be reset somehow??

Dave

[rickyboy]

Thanks for the reply James. Probably didn,t ask the question in the right way. What I want to know is if I clear the fault cause, will I still read out the error 15 when I do the paper clip test, or does the fault memory need to be reset somehow??

Dave

Yep, does need to be reset.  Usually 25-30 starts with no EML will clear the memory.  You can do this by turning the ignition onto position 2 then off and repeat as many times.

[TheBoy]

Seems to be a lot of poor diags going on here - if the ecu is complaining about cts values being implausible, then that is what needs checking first.  Absolutely no point at this stage looking at other problems until this one is fixed - if the ecu is having to put guessed default values in, it will never run well.

[rickyboy]

Seems to be a lot of poor diags going on here - if the ecu is complaining about cts values being implausible, then that is what needs checking first.  Absolutely no point at this stage looking at other problems until this one is fixed - if the ecu is having to put guessed default values in, it will never run well.

Pretty sure he's saying that the EML is out, he just is wondering why the code 15 is still there when he paperclips.